1. Field
The invention is closely related to coherent laser radar and rangefinding devices. Owing to the very short wavelengths involved, these devices can detect not only position and translation but vibration modes of an active target.
2. Prior Art
Laser radars (LIDAR's) have proven to be effective adjuncts to RADAR's, having better spatial and doppler resolution due to the short wavelength. RADAR is clearly better for extremely long range applications where distances are measured in tens of kilometers. In the measurement of target vibration modes at distances of up to a few kilometers the short wavelengths of LIDAR made it clearly superior. Various pieces of equipment can readily be identified at these distances by a very broad spectrum of characteristic vibration frequencies. Variations in these characteristic frequencies can be used to identify age, loading and other factors that affect the equipment during its useful life.
To best record the above patterns the vibration sensor system has been mounted on an acoustically quiet fixed platform. There are, however, many applications wherein it would be advantageous to make these measurements from a moving platform. Particularly, it would be desirable to be able to make vibration measurements from an aircraft which moves quickly and can reach otherwise inaccessible areas. The added vibration supplied by such moving platforms, however, masks the desired data. The vibrations of the platform could be measured and recorded separately and subtracted from the measurements made on the target, but this would be a complex and costly procedure.